Comtech EF Data SMS-758 - Manual (Page 108)

Theory of Operation SMS-758 Modem Protection Switch
4–48 MN/SMS758 Rev. 3
4.9 IF Switch
The IF switch is a 14” x 5” module that fits in the upper rear section of the switch
chassis. The IF switch isolates the backup modulator’s IF outputs, and connects the
backup modulator’s output in place of any of the prime modulators when a fault is
detected. The IF switch also connects the IF backup demodulator’s inputs to one of the
downlink inputs. Refer to Figure 4-21 for a block diagram of the IF switch board.
4.9.1 Specifications
Power source +12V
Isolation >60 dB
Balance ± 0.25 dB
Loss <1 dB
4.9.2 Theory of Operation
The IF switch contains 22 baseball switches that comprise the IF switching matrix. Each
baseball switch is controlled separately by the M&C card via the switch driver card.
The modulator section of the switching matrix contains 16 of the switches that control
the backup modulator outputs, to switch to any of the eight prime modulator outputs if a
fault is detected by the M&C card. The operator can also manually select a backup
modulator to switch in for any of the prime modulators via the front panel (refer to
Section 3.2.5.3).
The demodulator section of the switching matrix contains the remaining six switches.
They connect the IF backup demodulator inputs to any of four or seven downlink inputs
for use when any of the prime demodulators are faulted. The operator can also manually
select a backup demodulator to be online for any of the prime demodulators via the front
panel.